Geoffrey Lean is Britain's longest-serving environmental correspondent, having pioneered reporting on the subject almost 40 years ago.

The campaigner-prince who has reinvented the role of the heir to the throne

Prince Charles, who turns 65 on Thursday, is probably the longest serving, most effective – and most abused – environmental campaigner in Britain. In my latest column in the Daily Telegraph, which contains video interviews with leading environmentalists who have worked with him, I review his long record of being ahead of his time on a range of green issues – thus redefining his role as Prince of Wales – and ask whether, at times, his efforts may have got a bit close to the constitutional knuckle.